This invention relates to a perforating cylinder for punching a series of holes in paper material and in particular is directed to a cylinder for perforating postage stamps.
Postage stamps are typically printed at the Bureau of Engraving and Printing from a continuous roll of paper 181/2" wide. After printing, the stamps are perforated by a perforating assembly comprising cooperating male and female cylinders. Typical dimensions of either the male or the female cylinder is a diameter of 13" or 143/8" and a width of 22" or 26".
The male cylinder has from 17,000 to 22,000 protruding pins arranged in symmetrical patterns on its outer surface. The female cylinder has an identically arranged set of holes on its outer surface. As the male cylinder and the female cylinder rotate in unison the protruding pins mesh with the corresponding holes. When the printed stamps are passed between the two rotating cylinders, the coaction of the protruding pins and the corresponding holes provide the desired perforating function.
The pins experience heavy wear and generally fail by getting dull or by breaking off. Either condition results in less than complete perforation of the stamps. A few ramdomly located dull or broken pins can be tolerated, but when several adjacently located pins become defective or when the total number of defective pins becomes excessive, the defective pins must be replaced.
On the prior art perforators, the pin replacement procedure is a lengthy one requiring up to 210 man hours of labor and a down time of approximately 2 days. Because of the unscheduled nature of the down time caused by the pin replacement procedure, the entire manufacturing process is adversely affected and production costs for stamps are driven upward.